This invention relates to electro-optic devices for vehicles and, more particularly, to an enhanced vehicular rearview mirror or window glazing incorporating an electro-optic medium allowing variation in the transmission of light in response to application of an electric field to the electro-optic medium.
Specifically, in one aspect, the invention is a variable reflectance, electro-optic mirror including protection against laceration injuries and scattering of glass or other fragments if broken or damaged, against degradation from ultraviolet radiation, and against fogging and misting in high humidity conditions.
This invention also relates to glazing in vehicles and, more particularly, to an enhanced vehicular window, sun visor, shade band or sunroof incorporating an electrochromic medium allowing variation in the light transmitted by the glazing in response to application of an electric field to the electrochromic medium. Specifically, the invention is a variable transmission, electrochromic vehicular window including protection against laceration injuries and scattering of glass, other fragments, or chemicals if broken or damaged, against degradation from ultraviolet radiation, and including thin film means to reflect a substantial portion of incident, solar, near-infrared radiation. Optionally, and preferably, the electrochromic glazing assembly is blue or green in transmission, as viewed from the vehicle interior, so as to reduce glare from the sun and to optimize visibility and a true-to-nature blue view of the sky.
In a collision, the glass typically used as the substrate in vehicular rearview mirrors poses potential hazards to the driver or other vehicle occupants. Since glass easily shatters into sharp, irregular fragments, there is a high likelihood of facial or other injury, typically lacerative in nature, in any collision. For this reason, prior known interior and exterior vehicular rearview mirrors, which typically consist of a single glass piece coated with reflective material, are conventionally protected by applying a tape or a plastisol-type plastic adhesive to the back surface of the glass piece. Accordingly, if impacted or broken in an accident, and shattered, glass fragments are retained by the tape or plastisol-type plastic adhesive.
More recently, however, a new generation of electro-optical mirrors has emerged which are fabricated using two pieces of glass separated by a gap or space which contains an electro-optic medium allowing variation in the light reflected by the assembly. For example, in liquid crystal rearview mirrors, the space between the transparent front and reflective coated rear glass pieces is filled with a semi-viscous liquid crystal material. In electrochemichromic or electrochromic mirrors, the gap or space contains a liquid, thickened liquid, gel or semi-solid material.
In these types of electro-optic, laminated mirror assemblies, scatterproofing of the rear glass piece is relatively easy since tape or plastisol-type plastic adhesives can be applied to its rear surface behind the reflective coating in the conventionally known manner. However, scatterproofing the front piece of glass in such a laminated assembly is difficult since the material used to fill the space between the front and rear glass pieces is usually insufficiently viscous or adhering to retain fragments of the front glass should it shatter in a collision.
Another problem encountered with electro-optic rearview mirrors and windows or glazing assemblies is degradation due to exposure to ultraviolet radiation over the life of the mirror or glazing. Ultraviolet (UV) radiation from the sun which penetrates the earth""s atmosphere has a wavelength in the range between 290 and 400 nanometers (nm) and can cause breakdown in the operational characteristics of the electro-optical medium including chain scission, cross-linking and stimulation of chemical changes in the chemicals used to formulate the electro-optical medium. This interferes with electronic conjugation in the aromatic conjugated materials typically used and thus the electro-optic activity of those materials is impaired. Moreover, the medium will often discolor taking on a yellowish tint visible in light reflected or passing therethrough and drastically affect the usefulness of the rearview mirror or window. Such degradation from UV solar radiation is particularly problematic in electro-optical automotive windows which are typically exposed to the full solar radiation, often when the electro-optical medium is in its colored state.
In order to overcome ultraviolet radiation degradation in such electro-optic rearview mirrors and glazings, it is possible to add UV radiation absorbing materials to the electro-optic medium. However, such UV absorbing additives, especially in higher concentrations and with broad UV absorbance, themselves impart a yellowish tint to the materials to which they are added. Such yellow tint is also visible in light reflected or transmitted therethrough. Yellow is aesthetically displeasing in many applications, and is particularly displeasing when used in rearview mirrors. Consumer acceptance of rearview mirrors having a yellowish tint or cast in the reflected light has been poor. Moreover, yellow mirrors are efficient reflectors of headlamp glare which itself is yellow. Consequently, prolonged exposure to sunlight and UV radiation, or reducing UV degradation in electro-optic mirrors with UV absorbing additives, can create negative consumer reaction and acceptance. Likewise, a yellow tint in, for example, an automotive sunroof is consumer displeasing as it detracts from the consumer""s appreciation of, and natural view of, the blue sky.
Another objective in the use of rearview mirrors is the matching of human sight sensitivity in various light conditions during the use of such mirrors to the glare sources and ambient lighting present. It is known that the spectral sensitivity of the human eye depends on its light adaptation. Thus, daylight and night driving conditions create differing human eye sensitivities. Further, nearly all night driving is affected by the reflection of light from the headlights of the driver""s own vehicle on the road. The electro-optic mirror assemblies of this invention should, therefore, optimally be constructed to correspond as much as possible with the eye sensitivities in both day and night driving conditions.
The electro-optic media commonly used in electro-optic mirrors and windows are often constituted of materials and chemicals of a potential toxic or otherwise hazardous nature. Should the mirror glass break in an accident, there is a possibility of automobile occupants contacting the electro-optic media, either directly or by contact with glass particles to which these potentially hazardous media are still adhering. Such contact presents a hazard to the occupants through toxic effects, and through skin irritation such as to eyes and facial areas. The anti-lacerative layers and laminate interlayers of this invention offer a barrier that ensures that contact with chemicals used within the mirror is minimized should the glass shatter in an accident.
Yet another problem is unwanted misting or fogging of the rearview mirror surface or the glazing surface when the vehicle encounters high humidity conditions. For example, in damp, cold conditions where the interior passenger compartment of a vehicle has a highly humid atmosphere, water droplets may tend to condense on the rearview mirror surface or window surface thereby obscuring vision in the mirror or through the window. Not only does such condensation prevent effective use of the mirror or window, but also requires frequent wiping by the vehicle driver which distracts his attention from driving.
Vehicular windows provide a field of view so that the driver can make safe driving decisions and allow occupants to comfortably view the surroundings. Glass vehicular sunroofs are luxury items that serve both aesthetic and functional needs. A transparent sunroof is primarily consumer-selected so that the occupants feel less claustrophobic and more linked to the outside environment. Sunroofs have a functional benefit in that, when opened, they can greatly increase cabin ventilation and so substitute somewhat for air-conditioning.
As reviewed in the publication SMART WINDOWS FOR AUTOMOBILES by Niall R. Lynam, SAE paper #900419, Society of Automotive Engineers, International Congress and Exposition, Detroit, Mich., Feb. 16-Mar. 2, 1990, the disclosure of which is hereby incorporated by reference, increases in the area of windows used in automobiles coupled with down-sizing of vehicular air-conditioners and environmental concerns associated with use of halocarbons in air-conditioners, have led to an increased need to use solar heat-load reducing glazing in vehicles. Since solar energy (for solar mass 2) is, on the average, 3% ultraviolet (UV), 48% visible radiation, and 49% near-infrared (NIR) radiation, nearly one-half of the solar energy can be eliminated without any loss in visibility.
Solar-energy reducing glazing is already in use on automobile windows and is based on two principles: modification of the glass composition to increase the infrared absorption; and deposition of single and multilayer coatings to reflect or absorb infrared radiation. In a vehicle, the glazing need not be concerned with heat insulative properties such as are required for solar efficient windows in buildings and homes. Building solar windows allow as much of the solar spectrum as is possible to transmit into the room but also trap this solar energy by acting as a heat mirror for energy radiated from walls, floors, furniture, etc.
With respect to a vehicle, heat built up when parked or driven in sunny climates is the principal concern. Thus, the solar glazing used in vehicles should, ideally, reflect away all of the incident near-IR solar radiation above around 800 nm since visible light is between about 400 and 800 nm. Even with such reflection, however, the approximate 50% of solar energy contained in the UV/visible spectral region, if transmitted, can contribute to heat buildup within the vehicular cabin.
Chromogenic materials have been suggested for providing electrically variable control over solar transmission in automobile windows. SAE paper #900419 discloses a variety of possible designs and constructions, among them being designs using liquid crystal or electrochromic materials. Liquid crystal designs, and particularly those that operate by scattering light rather than by absorbing/reflecting light, however, yield only moderate solar energy benefit when used in automobile glazing. Electrochromic windows, because they do not operate by a light scattering mechanism, are preferred for use in variable transmission solar-efficient automobile window glazing.
A wide variety of infrared attenuating means including those that operate principally by reflecting varying amounts of the near-IR region, or by absorption, also have been disclosed in the prior art. Some have been used in association with variable transmission liquid crystal panels. For example, U.S. Pat. No. 4,749,261 to McLaughlin et al. describes a liquid crystal material operable to modulate light transmitted through a panel such as a sunroof, window, or partition. The liquid crystal material selectively operates to transmit or to scatter light.
McLaughlin et al. describe an embodiment which includes an infrared light reflective material which may take the form of a stainless steel or tin oxide, optically transparent, infrared reflecting, and electrically conductive coating that preferentially reflects infrared light while allowing visible radiation to pass. McLaughlin et al., however, fail to explicitly distinguish to which portion of the infrared spectrum (i.e., near-IR between 800 nm and 2500 nm or IR above 2500 nm) their invention is directed, and fail to combine that revelation with an electrochromic medium. Other references have failed to distinguish the particular needs of vehicular variable transmission glazing from variable transmission glazing usable as building windows and the like.
Accordingly, a need is apparent for a laminate electro-optic vehicular rearview mirror and glazing assembly which can be effectively scatterproofed to retain glass fragments from both glass pieces in the assembly, protected against lacerative-type injuries, protected against ultraviolet radiation damage throughout its life, and protected against annoying fogging and misting of the interior cabin surface in high humidity conditions. In addition, there is a related need for electro-optic rearview mirror assemblies which provide reflected light of a commercially and consumer acceptable color or tint and which match human sight sensitivity in both day and night conditions to the glare sources and ambient lighting present.
In addition, a further need is apparent for a combination near-infrared attenuating/electrochromic window which maximizes solar attenuation performance while allowing maximum variability of visible light. There is also a related need for a vehicular window which combines an electrochromic medium which attenuates visible light by absorbance and/or reflection with an efficient near-infrared reflector and an ultraviolet reducing means. Further, there is a related need for a solar attenuating window which can be effectively scatterproofed to retain glass fragments from the glass pieces in the window, protected against lacerative-type injuries, protected against leakage of chemicals, protected against ultraviolet radiation damage throughout its life, and protected against annoying fogging and misting of its surface in high humidity conditions.
The present invention overcomes the above problems by providing a laminate electro-optic vehicular rearview mirror which is protected against scattering of glass or other mirror element fragments if broken or damaged in a collision while reducing the risk of laceration from contact with the front glass or other element. In addition, the assembly is protected against degradation by ultraviolet radiation. The ultraviolet radiation reduction may be incorporated together with the scatterproofing, anti-lacerative protection. Further, the assembly may incorporate anti-fogging/anti-misting materials which prevent or reduce condensation and fogging in high humidity conditions.
In one form, the invention is an anti-lacerative, scatter protected, laminate, electro-optic rearview mirror assembly including first and second spaced optically transparent elements mounted in a mirror case. The elements each have front and rear surfaces defining a space between the rear surface of the first element and the front surface of the second element. An electro-optic medium is included in the space and has a light transmittance variable upon application of an electric field. Means are provided for applying an electric field to the electro-optic medium to cause variation in the light transmittance thereof. A reflective coating is included on one surface of the second element and is adapted to reflect light incident thereon through the first element and the electro-optic medium. A layer of optically transparent, tear/perforation resistant material is adhered to the front surface of the first element for retaining and preventing scattering of fragments from that element in the event of damage or breakage and for reducing risk of laceration from contact with the first element if damaged or broken.
The optical elements may be glass or plastic. The anti-lacerative, anti-scattering layer preferably is a sheet of polymer material such as reticulated polyurethane. In order to reduce ultraviolet radiation transmitted into the assembly, the polymer may be a combination of polyvinylbutyral and polyester which has ultraviolet radiation reducing properties. Alternately, the anti-lacerative layer may incorporate ultraviolet radiation absorbing, blocking or screening additives selected from the group including benzophenones, cinnamic acid derivatives, esters of benzoin acids, salicylic acid, terephthalic and isophthalic acids with resorcinol and phenols, pentamethyl piperidine derivatives, salicylates, benzotriazoles, cyanoacrylates, benzilidenes, malonates and oxalanilides which may also be combined with nickel chelates and hindered amines. These additives also stabilize the anti-lacerative layer itself against ultraviolet degradation.
Another UV radiation reducing alternative is the use of a clear, transparent UV transmission reducing coating preferably applied to the front surface of the front glass element followed by the anti-lacerative, scatterproofing polymer layer.
It is also possible to incorporate a sheet polarizer with the anti-lacerative layer, or apply a dichroic, reflective filter material to the glass element which provides wide band ultraviolet radiation reduction. Examples of such filters include thin film stacks.
It is also possible to substitute a laminated glass assembly for the front element, such assembly including a pair of glass panels adhered to one another with a sheet of polyvinylbutyral or sheet polarizer which have ultraviolet radiation reducing qualities. An anti-lacerative layer may be applied to the front surface of the first of the two glass panels in such a laminate.
A second form of the invention is a reduced ultraviolet radiation transmitting laminate electro-optic rearview mirror assembly which also includes first and second spaced optically transparent elements, an electro-optic medium therebetween, means for applying an electric field to the electro-optic medium and a reflective coating on one surface of the second element. In this form, ultraviolet radiation reducing means are incorporated in the assembly for reducing transmission of ultraviolet radiation into the electro-optic medium and the assembly.
Preferably, such ultraviolet radiation reducing means may include glass having an increased iron oxide or cerium oxide content or other specialized glasses such as blue or green tinted glass which are highly transmitting in the visible portion of the electromagnetic spectrum but have greatly reduced transmission in the ultraviolet portion of the electromagnetic spectrum. Anti-lacerative layers may be adhered to the front surface of such UV reducing glass to both strengthen the glass and provide anti-lacerative, scatterproofing properties. When such anti-lacerative layers are used, similar UV absorbers, blockers and screening materials may be incorporated in such layer. Alternately, sheet polarizers, transparent, UV reducing coatings, and UV radiation dichroic reflective filter materials may be used or added. Anti-fogging additives may also be included.
In addition, the ultraviolet radiation reducing means may include a laminated assembly incorporated as the front or first element of the mirror assembly and include spectrally selective absorbing means for absorbing more light in those regions of the visible spectrum from about 560 nanometers to about 780 nanometers than is absorbed in those regions of the visible spectrum from about 400 nanometers to about 560 nanometers. Such spectrally selective absorbing means may include blue or green tinted specialized glass or blue or blue/green tinted polymeric interlayers adhering the panels of the laminate front element together. In addition, coatings or layers of UV radiation reducing paint or lacquer or polymeric films may be included on the interior, facing surfaces of the laminate. Alternately, the panels of the laminate first element assembly may be adhered via a moderate to low modulus of elasticity adhesive layer which is preferably poured between the panels, cured with ultraviolet radiation, and which preferably includes an index of refraction similar to that of the glass panels to reduce distortion.
It is also possible to incorporate UV radiation reducing additives directly in the clear plastic when such plastic is used to form the first optical element. Alternately, UV reducing additives can be added to the electro-optic medium for UV stabilization.
The present invention also provides a combination near-infrared attenuating, electrochromic glazing assembly which is protected against scattering of glass or fragments if broken or damaged in a collision while reducing the risk of laceration from contact. Further, protection is offered against contact with the chemicals used in the electro-optical medium should the assembly be damaged in an accident. In addition, the window assembly is protected against degradation by ultraviolet radiation. The ultraviolet radiation reduction may be incorporated together with the scatterproofing, anti-lacerative protection. Further, the window assembly may incorporate anti-fogging/anti-misting materials which prevent or reduce condensation and fogging in high humidity conditions.
In one form, the invention is an anti-lacerative, scatter protected, electrochromic glazing assembly including first and second spaced optically transparent elements. The elements each have inside and outside surfaces defining a space between the outside surface of the first element and the inside surface of the second element. An electrochromic medium is included in the space and has a light transmittance variable upon application of an electric field. Means are provided for applying an electric field to the electrochromic medium to cause variation in the light transmittance thereof. Near-infrared reflective means are located on at least one of the first and second elements for reducing the transmission of near-infrared radiation through said window assembly. The reflective means incorporate at least one semi-transparent, elemental, thin metal film which reflects at least about 30% of the solar energy for Air Mass 2 in the spectral region from 800 nanometers to 2500 nanometers. In a preferred embodiment, the thin metal film has a physical thickness of between about 80 angstroms and 300 angstroms and, preferably, of sheet electrical resistance of no greater than about 8 ohms/square.
The optical elements for the glazing assembly may be glass or plastic and may employ the same anti-lacerative, anti-scattering, absorbing/filtering, tinting and ultraviolet reducing means listed above for the optical elements of the electro-optic mirror. It is also possible to substitute a laminated glass assembly for the inside element or the outside element, such assembly including a pair of glass panels adhered to one another with an interlayer such as a sheet of plasticized polyvinylbutyral or equivalent which has ultraviolet radiation reducing qualities. An anti-lacerative layer may be applied to the inner surface of the first or innermost of the two glass panels where the first element is such a laminate.
In preferred forms, the near-infrared reflective elemental thin film is sandwiched between optically transparent layers consisting of metal oxide, nitride, halide, or sulfide thin films. These thin films serve as an undercoat to the thin metal film to enhance its bonding to the substrate and as a visible light anti-reflection overcoat to enhance visible light transmitivity. The elemental thin metal film is preferably elemental silver or a silver alloy such as with copper but with the silver being the majority component. Gold, copper, or aluminum are alternate choices.
Accordingly, the present invention recognizes and applies novel protective concepts to laminate, electro-optic vehicular rearview mirrors and glazings not previously obtained. The invention solves three difficult problems encountered in prior commercialization of laminate electrochromic mirrors, namely, scatter protecting the front glass element, reducing lifetime ultraviolet degradation problems arising from the UV instability of the typical electro-optical medium sealed between the glass elements, and reducing fogging or misting caused by condensation in high humidity conditions. Further, the invention enhances the aesthetic appearance and customer acceptance of UV stabilized, electro-optic rearview mirror assemblies which would otherwise reflect light with a yellow tint by absorbing light in the yellow/orange/red regions of the visible spectrum to produce a commercially acceptable silvery or silvery-blue reflection. Further, the invention matches human sight sensitivity in both day and night conditions for either inside or outside mirrors to the glare sources and ambient lighting present by incorporating means causing light reflection in the blue region of the visible spectrum and thus well-suiting the mesopic human vision range. In addition, these results are obtained in an economical manner easily incorporated in existing rearview mirror cases requiring no specialized supports or surrounding apparatus in the vehicle.
The present invention also recognizes that maximum solar attenuation performance can be obtained through the combination of novel near-infrared attenuating concepts and electrochromic concepts while maintaining maximum variability of visible light. The glazing assembly incorporating the near-infrared attenuating and electrochromic means also incorporates the novel protective concepts listed above which solve for glazings or windows the similar problems encountered in prior commercialization of laminate electrochromic mirrors, namely, scatter protection, reduction of ultraviolet instability of the typical electrochromic medium, and diminution of fogging or misting problems. Further, the solutions suggested for masking the yellow tint caused by ultraviolet reductors are applicable to the window assembly.
These and other objects, advantages, purposes and features of the invention will become more apparent from a study of the following description taken in conjunction with the drawings.